Six-month old Boo was taken into the care of the Bracknell and Wokingham Districts branch of Cats Protection on Friday night, after she was found abandoned in a Warfield park.
A passing walker realised the box was not all it seemed when her dog started sniffing and making a fuss of it. She opened it to find Boo - so named because of her big eyes and ghost-like appearance - cowering inside.
Lynne Pothecary, publicity officer for the Cats Protection branch, said: "Had it not been for the dog being so interested in the box, this poor little cat's fate could have been horrific. Either left to die with no-one even realising or being thrown in a refuse truck."
She added Boo is friendly but extremely hesitant as a result of what is believed to be "another example of shocking animal mistreatment" and a fosterer is currently working on gaining her trust. "Boo seems in good condition, but if this was a horrid prank no distraught owner seems to be searching for her," she said.
"We expect we will never find out why Boo was in the box - we can only look for a bright and safe future for her by finding her a loving home, once she has been neutered, vaccinated and microchipped."
And thanks to an appeal on Facebook, the branch has already found a potential new home for beautiful Boo.
But with the arrival of Boo - among many other cats - and the current financial climate the Bracknell and Wokingham Districts branch is struggling to cover veterinary and food costs.
Donations can be made via www.justgiving.com/Cats-Protection-Bracknell-and-Wokingham-Districts
Alternatively people can donate either £2, £5 or £10 via text message, text BWCP99 to 70070 followed by the donation amount.